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1194 R. C. KENMla lour.AWWA day water cure is desirable for hy- draulic structures, but less expensive curing methods have proved reasonably satisfactory for floors and walls. With formed concrete members it is essen- tial that the forms be kept wet until stripped. Immediately after stripping, the concrete must be either covered with wet curing blankets for the dura- tion of the curing period or coated with an appropriate curing membrane. Application of the curing blankets or curing membrane should not be post- poned until cone holes are filled or other repairs are made. In the case of buried concrete reservoirs, an ex- cellent system of curing and water- Fig. 13. Typical Sealant Groove proofing consists of coating the sur- face, immediately after finishing, with a heavy coating of asphalt -emulsion, fol- lowed by a coat of whitewash after the asphalt -emulsion has set; after the con- crete has set (J-1-in.), curing blankets are placed on the roof surface and kept saturated with water until the earth blanket is placed. By keeping the blankets saturated, the concrete slab is kept cool. This is important in a large reservoir because if the tempera- ture rise of the concrete is substantial, the expansion may be enough to induce excessive stresses in the walls and pos- sibly cause cracking. Testing Concrete Reservoirs It is advisable to fill the reservoir for testing purposes before any back - fill is placed and to leave it full while the backfill is placed. Although very heavy equipment, such as loaded carry- alls, should never be permitted to oper- ate near the walls, there is less danger of cracking the walls by filling the reservoir first if heavy equipment should inadvertently get too close to the walls. The ability of concrete to seal hair- line cracks through autogenous healing is truly remarkable if a few simple pro- cedures are followed. These include: 1. Using at least six sacks of cement per cubic yard Waterstop Extend Sealant Under Wall and Bond to Waterstop iSealant Groove at Fig. 14. Waterstop and Sealant at Foot. ing-Wall .Taint 2. Filling the reservoir very slowly by raising the water level about 1 foot/ day so as to give the concrete an op- portunity to absorb water. The swell- ing that results reduces the widths of any cracks that may have been formed 3. If any cracks or honeycombed areas in the walls are wide enough to allow trickles of water to flow through the walls, such flows should be stopped by calking the outside face of the wall with lead wool so as to permit autog- enous healing to take place. If this is not done, the flow may never stop because the cement, as it is leached out of the concrete, is continually washed away. RICHARD BRADY &ASSOCIATES, INC. F-63 25B-141